On the other hand, what if we have a topic of research that has a large potential for great benefit and a small potential for evil (it's a hypothetical example, so don't worry about how we know the precise degree to which each potential is a possibility). Say the researchers involved stop work on the grounds that they find it unacceptable to take the risk of it being used for unpleasant purposes and destroy their data to help prevent anyone else doing the same thing, thereby denying society of the possible benefits of their research. Are they right or wrong?

I'm inclined to think that the best way of dealing with it is to do the research and then let society deal with it. What right do scientists (myself included) have to make decisions on behalf of everyone else on the planet? We can have opinions and argue for them, but why should our opinion count for more than that of 6 billion other people? Science does not exist in order to make decisions on behalf of other people, it exists to give those people options that they would not otherwise have. Some of those options include the ability to wipe out the entire population of the planet or make us all tall, blond and superintelligent. What everyone does with these options is up to them.

Which is more wrong - performing the research that makes the nuclear bomb possible, or forcing my personal morality onto everyone else on the planet?

I possibly didn't make that very clear. I'm absolutely against scientists making decisions about their research based on how they think everyone else in the country will receive it. Annoyingly, the media often seems to have other ideas. I'd also argue that furthering knowledge results in options being made available that wouldn't otherwise be, even if it's only at the level of "Do I want to understand this or not?" :)